Many studies on planning and operation of reservoirs for power production rely on the operational strategy from the United States Army Corps of Engineers (“USACE”) described in reference EM-1110-2-1701 entitled “Engineering and Design, Hydropower” (the “USACE Reference”), which aims to preserve the firm energy of the reservoir and then to produce secondary energy. The operational strategy presented is based on two aspects: (a) the actual control strategy, and (b) a set of control values of the reservoir level, which acts as a threshold in the decision-making process, and is called the Rule Curve. This Rule Curve has one parameter, which is the current month of the year (it is a 1-parameter set), and gives a control value of the reservoir level at the end of each calendar month.
The operational strategy to use with this set of control parameters is simple, stated as follows: (i) at the beginning of the current month simulate the operation of the reservoir/powerhouse generating only the continuous power and firm energy; (ii) if the simulated end-of-month level in the reservoir falls below the control value, generate only the firm energy and continuous power; (iii) if the simulated end-of-month level is greater than the control value, generate as much energy as possible until the level reaches down to the control value, always limited by the power-plant capacity. The set of control values is fixed over the years and gives one control value of the end-of-month reservoir level for each calendar month.
The Rule Curve and the continuous power/firm energy yield are obtained by a recursive backward simulation algorithm until the maximum firm yield and continuous power are obtained. The calculation of the continuous power/firm energy yield is made by trial-and-error, generating only the trial continuous power under the assumed daily operation pattern, and calculating the required level at the beginning of each time period considering the reservoir at the minimum power pool level at the end of the time series; the reservoir fails if it requires a level greater than the maximum power pool level. This backward simulation is repeated until the maximum continuous power/firm energy yield is obtained.
The Rule Curve is the envelope of the maximum end-of-month levels obtained in the backward simulation which gives the firm energy yield and continuous power. As a by-product of this procedure, at least one value of the Rule Curve is the top of the power pool. The Rule Curve can be updated periodically as more hydrological information is collected during the actual operation of the reservoir, or bathymetric studies are undertaken to analyze sediment deposition and update the reservoir elevation-area-storage curve, or other significant event occurs.
FIG. 1 shows a typical Rule Curve (RC) for a reservoir, following the USACE guidelines. It shows also the minimum and maximum power pool levels, and the general recommendation for operation of the power-plant. Note that one level of the Rule Curve equals the maximum normal power pool level. As can be seen, under the USACE operational strategy, the control of the reservoir operation depends only on the current time of the year. There is no influence of the current state of the reservoir system in the selection of the value of the end-of-month control level, nor is there an explicit maximization of the mean energy generated by the reservoir.